This invention is related to the method of making heat-resistant polyester of high degree of polymerization with reduced end carboxyl group (hereinafter this is written as COOH).
Various methods of reducing COOH of polyester have been proposed. Recently the method of reacting polyester and bis-oxazoline compound has attracted attention.
For example, Kokai JP No. 59525 - 1975 proposed the method in which phenylenebisoxazoline compound was added to the polyester before spinning. It was said that use of this method reduces the COOH of polyester, gives the effect of increasing the molecular weight and offsets at least a part of the decomposition which occurs at the time of spinning.
However, in this method, the melt spinning is done after adding the powder of bisoxazoline compound to the polyester chips; thus, it adds a process of solidifying the polyester and making chips. In addition, the remelting causes the decomposition of polyester and this is not offset sufficiently, resulting in some reduction in the molecular weight and insufficient effect of reducing the COOH.